Presently used methods of determining the stimulus necessary to activate a go, no-go device such as an electroexplosive device requires the destructive testing of a large number of the devices. Previously used techniques for evaluating the sensitivity of electroexplosive devices (EED) have incorporated a form of the well established Bruceton test by applying a known fixed value of voltage, current, or energy in the form of a step function to the EED and observing the results (go or no-go testing). This type of sensitivity testing is characterized in that the item will respond or will not respond to the stimulus (go, no-go). In effect the output is a binary or step function of the input as opposed to a proportional relationship. The test is destructive. If the device does function, it is mechanically destroyed by the explosive output. If the EED does not function, its characteristics are altered, which eliminates application of a higher stimulus level to that device as meaningful data in determining its response level.
The probability of response of an EED increases with the level of the stimulus. The functioning characteristics of an EED are determined by sensitivity testing. The type of electrical stimulus used is dependent upon the parameters of interest and the intended application of the device. The most common types of stimuli are constant voltage, constant current, and capacitive discharge. Constant voltage stimulus is typified by a lead acid car battery. An ideal power source of this type is capable of supplying infinite current with no source voltage drop. A constant current source provides a fixed current at whatever voltage the electrical load requires. It can be approximated by a voltage source having an extremely large series resistance compared to the load resistance. In many EED applications a capacitor is used to function a particular EED. The purpose of this type stimuli is to apply a known, predetermined amount of energy to the device. The energy may be calculated by the equation E = 1/2CV.sup.2, where V is the voltage that the capacitor is charged to and C is the value of capacitance.
The desired sensitivity test is selected on the basis of the particular parameters of interest (voltage, current, energy) and the stimulus is then determined. The objective of the test is to determine the device characteristics with respect to the particular parameter. A sample lot of the device which is representative of the entire device population is then obtained and tested. From these results a prediction is obtained as to how a device selected at random from the entire population should respond.
The most commonly accepted technique for sensitivity testing presently incorporates the well known Bruceton method, which is discussed in the "Ordnance Engineering Design Handbook," ORDP 20-11, page 10-22. Given a sample lot, this technique consists of increasing the stimulus level, in predetermined increments, to the point where the particular EED fires. The stimulus is then decreased by an increment, usually the amount of previously advanced increment if it is known, and another EED is tested. If this device does not function, the stimulus level is again increased by the fixed increment and applied to yet another item. This process is repeated with successive EED's having only one level of stimulus applied thereto until a unit or device fires. The stimulus level is then sequentially decreased with respective EED's until a unit does not fire. The Bruceton method also contains a procedure for obtaining the mean firing current or stimulus and its deviation. The analysis is based on the assumption that deviation of the firing current distribution is a normal or Gaussian type. If it is not the case, the data must be made Gaussian by the introduction of a normalizing factor. In testing EED sensitivity, the data is made to appear Gaussian by using the logarithm of the stimulus. This testing method has the advantage of concentrating the testing about the fifty percent probability firing point. It is noted that these sensitivity testing methods will not reveal the presence of a defective sample, such as a unit with a missing bridgewire. They merely indicate that an EED did not fire, leading to the possibly erroneous presumption that only a higher level of stimulus was required to fire the device.